Day-night differences in the number of pineal "synaptic" ribbons in two diurnal rodents, the chipmunk (Tamias striatus) and the ground squirrel (Spermophilus richardsonii).

Daytime numbers of pineal "synaptic" ribbons higher than reported in the pineal gland of any other mammalian species were observed in two diurnal rodents, the eastern chipmunk and Richardson's ground squirrel. The number of "synaptic" ribbons was lower during the daytime and higher at night in both of these species.